Insulin-Like Growth Factor I

Caloric restriction (CR) may retard aging processes and extend lifespan in organisms by altering energy-metabolic pathways. In CR rodents, glucose influx into tissues is not reduced, as compared with control animals fed ad libitum (AL), although plasma concentrations of glucose and insulin are lower. Gene expression profiles in rodents have suggested that CR promotes gluconeogenesis and fatty acid biosynthesis in skeletal muscle. In the liver, CR promotes gluconeogenesis but decreases fatty acid synthesis and glycolysis.

Caloric restriction (CR) and a reduced growth hormone (GH)-insulin-like growth factor (IGF-1) axis are associated with an extension of lifespan across taxa. Evidence is reviewed showing that CR and reduced insulin of GH-IGF-1 axis may exhibit their effects at least partly by their common stimulatory action on autophagy, the cell repair mechanism responsible for the housekeeping of cell membranes and organelles including the free radical generators peroxisomes and mitochondria.

XPF-ERCC1 endonuclease is required for repair of helix-distorting DNA lesions and cytotoxic DNA interstrand crosslinks. Mild mutations in XPF cause the cancer-prone syndrome xeroderma pigmentosum. A patient presented with a severe XPF mutation leading to profound crosslink sensitivity and dramatic progeroid symptoms. It is not known how unrepaired DNA damage accelerates ageing or its relevance to natural ageing. Here we show a highly significant correlation between the liver transcriptome of old mice and a mouse model of this progeroid syndrome.

BACKGROUND: We review studies showing that CR acts rapidly, even in late adulthood, to extend health- and lifespan in mice. These rapid physiological effects are closely linked to patterns of gene expression in liver and heart. Non-human primate and human studies suggest that the signal transduction pathways responsible for the lifespan and health effects of caloric restriction (CR) may also be involved in human longevity. Thus, pharmaceuticals capable of mimicking the effects of CR (and other methods of lifespan extension) may have application to human health.

Proceedings of the National Academy of Sciences of the United States of America

Rather than being a passive, haphazard process of wear and tear, lifespan can be modulated actively by components of the insulin/insulin-like growth factor I (IGFI) pathway in laboratory animals. Complete or partial loss-of-function mutations in genes encoding components of the insulin/IGFI pathway result in extension of life span in yeasts, worms, flies, and mice. This remarkable conservation throughout evolution suggests that altered signaling in this pathway may also influence human lifespan.

Dampening of insulin/insulin-like growth factor-1 (IGF1) signaling results in the extension of lifespan in invertebrate as well as murine models. The impact of this evolutionarily conserved pathway on the modulation of human lifespan remains unclear. We previously identified two IGF1R mutations (Ala-37-Thr and Arg-407-His) that are enriched in Ashkenazi Jewish centenarians as compared to younger controls and are associated with the reduced activity of the IGF1 receptor as measured in immortalized lymphocytes.

Insulin and insulin-like signaling regulate survival and lifespan in a variety of animal species, from nematodes and flies to higher vertebrates and mammals. Recently, it was shown that brain IGF-I receptor and brain IRS2 control mammalian lifespan, and that this occurs through neuroendocrine mechanisms, control of energy metabolism and modified stress resistance. Furthermore, it was demonstrated that insulin receptor substrate molecules are implicated downstream of insulin and IGF receptors in the extension of lifespan.

A recent report of virtually complete protection from diabetes and cancer in a population of people with hereditary dwarfism revived interest in elucidating the relationships between growth, adult body size, age-related disease and longevity. In many species, smaller individuals outlive those that are larger and a similar relationship was shown in studies of various human populations. Adult body size is strongly dependent on the actions of growth hormone (GH) and the absence of GH or GH receptor in mice leads to a remarkable extension of longevity.

Multicellular organisms are composed of an interactive network of various tissues that are functionally organized as discrete organs. If aging were slowed in a specific tissue or organ how would that impact longevity at the organismal level? In recent years, molecular genetic approaches in invertebrate model systems have dramatically improved our understanding of the aging process and have provided insight into the preceding question.

Caloric restriction, that is limiting food intake, is recognized in mammals as the best characterized and most reproducible strategy for extending lifespan, retarding physiological aging and delaying the onset of age-associated diseases. The aim of this mini review is to argue that p53 is the connection in the abilities of both the Sirt-1 pathway and the TOR pathway to impact on longevity of cells and organisms.